vagina size: WebMD says

The vagina is a very “elastic” organ, says Christine O’Connor, MD, director of adolescent gynecology and well women care at Mercy Medical Center in Baltimore. It is small enough to hold a tampon in place, but can expand enough to pass a child through. This is because the walls of the vagina are similar to those of the stomach, they have rugae, meaning they fold together to collapse when unused, then expand when necessary.

“It doesn’t stay one particular size,” O’Connor says. “It changes to accommodate whatever is going on at that time.”

The most commonly used measurements regarding the size of vaginas come from Masters and Johnson’s work from the 1960s. They looked at 100 women who had never been pregnant and found that vagina lengths, unstimulated, range from 2.75 inches to about 3¼ inches. When a woman is aroused, it increased to 4.25 inches to 4.75 inches. Regardless of how long the vagina is, the area that is thought to be important for most women’s sexual response is the outer one-third.